This invention is on the design, synthesis and bioassay of synthetic analogs of the luteinizing hormone releasing hormone (LHRH). The ultimate achievement was of analogs which function as antagonists of LHRH and which are adequately potent to inhibit ovulation, and have altered structural features which allow the release of only negligible amounts of histamine. Since there is no predictable synthetic approach to an antagonist of high potency and very low histamine release, it was necessary to explore diverse approaches to the objective in order to discover an approach to a combination of structural features which would yield an antagonist of high potency to inhibit ovulation and of very low activity of release histamine.